Eselect (OpenGL)

Introduction

Eselect (OpenGL) (also called eselect-opengl) is a module for Eselect that allows the OpenGL implementation on a Funtoo Linux or Gentoo Linux system to be switched between a variety of installed OpenGL implementations. It functions by creating an env.d file at /etc/env.d/03opengl which contains OpenGL settings, as well as managing symbolic links to OpenGL libraries and headers.

Sample env.d File

A sample env.d file for a multilib system with xorg-x11 OpenGL implementation may look like this:

Implementation

Eselect-opengl is implemented as a single bash-based Eselect module approximately 10K in size, installed at /usr/share/eselect/modules/opengl.eselect. One interfaces with this module via the main eselect command:

# eselect opengl help
Manage the OpenGL implementation used by your system
Usage: eselect opengl <action> <options>
Standard actions:
help Display help text
usage Display usage information
version Display version information
Extra actions:
list List the available OpenGL implementations.
set <target> Select the OpenGL implementation.
<target> The profile to activate
--use-old If an implementation is already set, use that one instead
--prefix=<val> Set the source prefix (default: /usr)
--dst-prefix=<val> Set the destination prefix (default: /usr)
--ignore-missing Ignore missing files when setting a new implementation
show Print the current OpenGL implementation.

What is Switched

Using eselect opengl set causes the following symbolic links to be updated to point to the files corresponding to the OpenGL implementation that you chose:

Libraries (32-bit and 64-bit):

/usr/lib(64)/libGL.so.*

/usr/lib(64)/libEGL.so.*

/usr/lib/(32|64|)/libGLESv1.so.*

/usr/lib/(32|64|)/libGLESv2.so.*

C Headers:

/usr/include/GL/*

/usr/include/EGL/*

/usr/include/KHR/*

/usr/lib(64|)/xorg/modules/extensions/libglx.so

The symbolic links point to an installed OpenGL implementation, stored inside /usr/lib(32|64|)/opengl/(implementation-name). These files are structured as follows:

Criticisms

Violation of Build Consistency

As documented in FL-1309, sometimes packages fail to merge when the "wrong" eselect opengl implementation is selected. This violates Portage's ability to consistently build a package from source, assuming all its dependencies are satisfied. This could be classified as a design bug -- eselect-opengl is functioning as intended, but its underlying theory of operation is not correct.

eselect-opengl-1.3* experiment

Introduction

As a result of FL-1309, an experimental solution was implemented in eselect-opengl-1.3*. With this version, all packages are built unconditionally against xorg-x11 OpenGL implementation and the other implementations are used only in runtime.

The rationale for this design change is that:

There should be a consistent and repeatable build/linking process for all OpenGL applications.

AMD and NVIDIA implementations of OpenGL are designed to be more of a "drop-in" runtime replacement for xorg-x11, rather than a standalone replacement for xorg-x11, and thus appear to exhibit more build-time bugs.

The env.d file has the same contents as the original one, except that the name was changed to ensure that the additional linker paths are added before the system paths where xorg-x11 libraries are installed.

The xorg.conf.d sets ModulePaths for non-xorg module replacements (such as the nvidia glx module), if necessary.

Issues

The widespread testing of eselect-opengl-1.3* has proven some issues with the new design:

xorg-server is unable to handle multiple occurences of Files section gracefully. Therefore, eselect-opengl's generated xorg.conf.d file collides with many user-defined configurations. (this has been patched locally and the patch is awaiting upstream review)

There are rumors of arm mali's prioprietary OpenGL implementations requiring applications to be built against its own GLES headers.